The present invention relates to center pivot irrigation systems and more particularly to angularity sensors incorporated therein to sense the angular deviation in the horizontal plane between adjacent span units to provide a signal proportional thereto to the controller controlling the movements of each span unit as it rotates about the center pivot whereby the plurality of articulated span units comprising the irrigation system are maintained in substantially preselected alignment as they rotate about the center pivot.
A center pivot irrigation system is shown in FIGS. 1 and 2 in top and side elevation views, respectively. In such a system, a fixed supported pipe 10 has a rotating pipe 12 mounted on one end with the opposite end connected to a source of water under pressure. A plurality of span units 14, 14' and 14", are connected end to end extending from the rotating pipe 12. Each pair of adjacent span units is interconnected by a flexible cylindrical boot 16. Each span unit comprises a substantially horizontal conduit 18 supported on the outboard end by a support tower 20 having wheels 22 thereon which are driven by a motor 24. At each junction between adjacent span units, a control mechanism, generally indicated as 26, is provided which provides a control signal proportional to the angular deviation between the adjacent span units. This control signal is used to control the motor 24 driving the wheels 22 associated with the inboard support tower 20. Each control mechanism 26 comprises an angularity sensor 28 connected to a controller 30 which, in turn, is connected to the associated motor 24. A plurality of sprinklers 32 are connected into the conduit 18 to disperse the water over the area being traversed as the span units 14, 14' and 14" revolve about the fixed support pipe 10.
Referring now to FIG. 3, the junction between two adjacent span units (for example 14' and 14") is shown. If the ground being traversed were a completely horizontal plane, angularity sensing to maintain the span units in a preselected state of alignment would be no problem. Unfortunately, agricultural land is more typically full of ruts, hills, etc. which impart a number of undesired forces on the span units. In FIG. 3, the axis X--X is the longitudinal axis concentrically through the conduit 18 of span units 14', 14" in perfect alignment. The line Y--Y is the line normal to line X--X passing through the midpoint of the junction of the two span units 14', 14". Line Y--Y, therefore, is also the tangent in the horizontal plane of the circle traversed by the junction between span units 14', 14" at the midpoint of their junction. Line Z--Z represents a line normal to both lines Y--Y and X--X and is, therefore, the vertical direction. A plane containing both lines Y--Y and X--X is, therefore, a horizontal plane when line Z--Z is normal to the earth's surface.
With reference to these lines then, one can see that the two conduits 18 can roll about their longitudinal axis (i.e. line X--X) as represented by the arrows 34. They can roll in the same direction equally or unequally or can roll in opposite directions. Likewise, because of linkages in the mechanical joining of the adjacent span units (not shown) and the flexibility of boot 16, the two conduits 18 can move toward and away from one another along line X--X as represented by the arrows 36. This is a longitudinal movement at the junction. A pitching movement is caused by relevant rotation between the two adjacent span units 14', 14" in the X-Z plane as indicated by the arrows 38. Likewise, again because of looseness in the mechanical linkage and the flexibility of the boot 16, there can be relative traverse movement along the line Y--Y as indicated by the arrows 40. Finally, there can be an angular displacement in the X-Y plane as indicated by the arrows 42. Of the five motions possible, individually and/or in combination, it is this latter angularity motion indicated by the arrows 42 which is the only one to which it is desired that the control system respond.
Several prior art angularity sensing systems are shown in FIGS. 4 through 9. In the system shown in top and side views in FIGS. 4 and 5, respectively, the conduits 18 are mechanically linked by members 44 and 46 with pin 48 disposed in hole 50. Lever arm 52 extends laterally from one conduit 18 and control unit 54 is mounted laterally extended in the same direction in the horizontal plane from the other conduit 18. A rigid control rod 56 is pivotally connected on one end to lever arm 52 and passes into control unit 54 on the opposite end. As the distance between lever arm 52 and control unit 54 changes due to positional changes between the two conduits 18, control rod 56 moves into and out of control unit 54 causing a change in the control signal therefrom. As an examination of the apparatus of FIGS. 4 and 5 will disclose, in addition to being sensitive to the angular motion of interest, this apparatus is also sensitive to roll, roll and pitch in combination, pitch (if the lever arm 52 is not placed close adjacent to the joint), and longitudinal slack.
Another popular prior art system is shown in FIGS. 6 and 7 in top and side views respectively. The connecting members 58 and 60 are provided with a ball and socket joint generally indicated at 62. A pair rigid arms 64 extend outwardly in opposite directions at the point of the ball and socket joint 62 lying in a horizontal plane. A flexible cable 66 extends from the end of one arm 64 around a spindle 68 to the end of the opposite arm 64 where it is connected. Spindle 68 is a rotating spindle connected as the input medium to the control unit 54'. As the two conduits 18 change position, spindle 68 is rotated by the flexible cable 66 to provide the appropriate change in signal from controller 54'. While this apparatus is responsive to the angular motion of interest, inspection will also reveal that it is sensitive, additionally, to transverse slack and a combination of pitch and roll.
Still another prior art system is shown in FIGS. 8 and 9 in top and side views respectively. In this system, a sensor arm, generally indicated as 70, is pivotally mounted on the conduit 18 having the control unit 54 mounted thereon. Sensor arm 70 is generally L-shaped. The arm portion 72 adjacent control unit 54 is connected thereto by a rigid control rod 56 in the manner of the apparatus of FIGS. 4 and 5. The other arm portion 74 of sensor arm 70 is an extended member which extends across the junction of members 44, 46 to contact the opposite conduit 18. Changes in angularity are, therefore, transmitted through sensor arm 70 to control rod 56 and thence to control unit 54. Since arm portion 74 is in rotatable and sliding contact with the opposite conduit 18, many of the problems of undesired signals from extraneous movement of the span units are eliminated which were associated with the apparatus described above. As will be seen, however, transverse slack still causes the apparatus of FIGS. 8 and 9 to produce erroneous angularity signals.
Wherefore, it is the object of the present invention to provide an angularity sensor for incorporation in such center pivot irrigation systems which is responsive only to changes in angularity in the horizontal direction between adjacent span units to thereby provide an accurate input to the control unit controlling the motors driving the respective span units.